Luminescent Properties of Green Phosphor Ca8Mg（SiO4 ）4 Cl2：EU^2＋ , DY^3＋ for LED Applications

The new phosphor calcium magnesium chlorosilicate, codoped with Eu^2＋ and Dy^3＋, was synthesized with the help of the high temperature solid state reaction in reducing atmosphere. The excitation and emission spectra were very similar to that of Ca8Mg（SiO4）4Cl2 ：Eu^2＋, and the Dy^3＋ concentration influenced the emission intensity of this phosphor. The intensity of Eu^2＋ and Dy^3＋ codoped CMSC was stronger than that of Eu^2＋ singly doped CMSC. The emission spectrum of the Dy^3＋ ion overlapped the absorption band of the Eu^2＋ ion, indicating that an energy transfer from Dy^3＋ to Eu^2＋ took place in CMSC：Eu^2＋, Dy^3＋ phosphor. The mechanism of the energy transfer from Dy^3＋ tO Eu^2＋, in this phosphor, might be resonant energy transfer.     

Preparation of Non-Grinding Long Afterglow SrAl2O4 ：Eu^2＋ , Dy^3＋ Material by Microwave Combustion Method

The non-grinding long afterglow material SrAl2O4：Eu^2＋ , Dy^3＋ was prepared by combustion method in home mierowave oven direetly, after dispersant, frother, eomburent, and mineralizer were added into the reacting system. XRD analysis showed that the powders were nearly pure SrAl2O4 phase with few other phases, and the size of the grain was 41.1 nm. Fluoreseenee speetrum results indieated that there were 2 exeitation peaks loeated at 345 and 400 nm, and the emission peak loeated at 516 nm, afterglow lasted up to 30 min or more. The mierowave eombustion method has advantages of less time, low temperature and no grinding process, and the material made by the method has good luminescent property.     

Preparation and Luminescence Properties of the New Long Phosphorescent Phosphors Ba1-x Cax Al2O4 ： Eu^2＋ , Dy^3＋

New long phosphorescent phosphors Ba1-x CaxAl2O4:Eu^2 , Dy^3 with tunable color emission were prepared and studied. The emission spectra show that the tuning range of the color emission of the phosphors is between 498 and 440 nm, which is dependent on x, under the excitation of UV. The wavelength of the afterglow increases with the increasing of x until x equals 0.6. The XRD patterns show that the single phase limit in the phosphors is below x value of 0.4.The Thermolumineseence spectra were measured to investigate the traps created by the doping of Dy^3 .     

Luminescence enhancement of BaMgSiO4：Eu^2＋ by adding borate as flux

The luminescence of EU^2＋ in BaMgSiO4 with BaB2O4 as flux was studied. The emission spectrum of the phosphor consisted of two bands, peaking at about 398 nm and 515 nm, which were attributed to the emissions from different Eu^2＋ sites in the lattice. When the BaB2O4 flux was applied, the intensity of the 398 nm emission was not clearly affected, but the intensity of the 515 nm emission was enhanced by about ten times. Gaussian fitting showed that the emission band at around 515 nm could actually be resolved into two bands with peak wavelengths of 499 nm and 521 nm, respectively. The assignments of the emission bands to the cation sites were carried out according to the values of bond valence. The overlapping of the 398 nm emission band on the excitation band of 515 nm emission implied that energy transfer could occur from the luminescent center related to the 398 nm emission to the center related to the 515 nm emission, and the energy transfer process remarkably enhanced the intensity of the 515 nm emission band. The phosphor had strong excitation at around 350-400 nm and emitted a bright green luminescence. Thus it could have applications as a green component in solid-state lighting devices assembled by near-UV Light Emitting Diodes （LED） combined with tricolor phosphors.     

A New Promising X-Ray Storage Phosphor BaBrCl：Eu^2＋

Photostimulated luminescence was observed in X-ray irradiated BaBrCl doped with Eu^2 ＋ . It shows an emission band that peak at 413 nm, and two difference absorption spectra （DAS） bands that peak at - 550 nm and 675 nm respectively. The stimulation energy is lower than that of BaFX：Eu^2＋ （X = Cl, Br）, and matches the cheaper, more portable, and more convenient semiconductor laser better. The results indicate that BaBrCl ： Eu^2＋ shows positive potential as a promising X-ray storage phosphor for practical utilization.     

Synthesis of Long Afterglow Phosphor CaAl2Si2O8 ：Eu^2＋, Dy^3＋ via Sol-Gel Technique and Its Optical Properties

The long afterglow phosphor CaAl2Si2O8：Eu^2＋ , Dy^3＋ was prepared by a sol-gel method. The sol-gel process and the structure of the phosphor were investigated by means of X-ray diffraction analysis （XRD）. It is found that the single anorthite phase formed at about 1000 %, which is 300 % lower than that required for the conventional solid state reaction. The obtained phosphor powders are easier to grind than those of solid state method and the partical size of phosphor has a relative narrow distribution of 200 to 500 nm. The photoluminescence and afterglow properties of the phosphor were also characterized. An obvious blue shift occurs in the excitation and emission spectra of phosphors obtained by sol-gel and solid state reaction methods. The change of the fluorescence spectra can be attributed to the sharp decrease of the crystalline grain size of the phosphor resulted from the sol-gel technique.     

Synthesis of Long Afterglow Phosphors MAI204：Eu^2＋ , Dy^3＋ （M=Ca, Sr, Ba） by Microemulsion Method and Their Luminescent Properties

Long afterglow phosphors MAl2O4：Eu^2＋ , Dy^3＋ （M = Ca, Sr, Ba） were synthesized by microemulsion method, and their crystal structure and luminescent properties were compared and investigated. XRD patterns of samples indicate that phosphors CaAl2O4：Eu^2＋, Dy^3＋ and SrAl2O4 ： Eu^2＋, Dy^3＋ are with monoelinie crystal structure and phosphor BaAl2O4：Eu^2＋ , Dy^3＋ is with hexagonal crystal structure. The wide range of excitation spectrum of phosphors MAl2O4： Eu^2 ＋ , Dy^3＋ （M = Ca,Sr, Ba） indicates that the luminescent materials can he excited by light from ultraviolet ray to visible light and the maximum emission wavelength of phosphors MAl2O4：Eu^2＋ , Dy^3＋ （M = Ca, Sr, Ba） is found mainly at λem of 440 nm （M = Ca）, 520 nm （M = Sr） and 496 nm （M = Ba） respectively, the corresponding colors of emission light are blue, green and eyna-green respectively. The afterglow decay tendency of phosphors can he summarized as three processes： initial rapid decay, intermediate transitional decay and very long slow decay. Afterglow decay curves coincide with formula I = At^ - n, and the sequence of afterglow intensity and time is Sr 〉 Ca 〉 Ba.     

Site Selective Spectroscopy of Suffactant－Assembled Y2O3：Eu Nanotubes

Y2O3:Eu nanotubes were synthesized by a surfactant assembly mechanism. Under ultraviolet-light excitation,the nanotubes present luminescence properties different from that of Y2O3:Eu nanoparticles. The peak position of the charge transfer band in excitation spectra varies with the monitoring emission peaks, while the emission spectra are dependent on the excitation wavelength. Laser selective spectroscopy was performed to distinguish the local symmetries of the Eu^3 ions in the nanotubes. The results of laser-selective excitation indicate that the emission centers near the surface of nanotube wails exhibit inhomogeneously broadened spectra without spectral structures while the two sites (site B and site C) inside the nanotube walls present resolved spectral structures. It is concluded by the number and peak positions of the spectral lines that the sites B and C possess different site symmetries.     

Preparation and photoluminescence of Tb^3＋ doped SrAl2O4 phosphor by composite combustion method

High-efficient Tb^3＋ activated SrAl2O4 phosphor was synthesized by a combined combustion-solid-state reaction method. The precursor of SrAl2O4：Th^3＋ phosphor was prepared via a combustion process, and then the as-prepared powder was heated in a reductive ambient of activated carbon at 1250 ℃ for 1 h. The results of X-ray diffraction, scanning electron microscopy, and photoluminescence spectra revealed the influence of the dosage of urea and heated process on the crystallinity, morphology, and photoluminescence of the phosphor. Comparing with traditional solid-sate reaction, the crystallinity and emission intensity of the SrAl2O4：Tb^3＋ phosphor were improved by this two-step process.     

Synthesis and Luminescence Properties of Gd2O3：Eu^3＋ Phosphors

Gd2O3: Eu^3 phosphors were prepared by urea homogeneous precipitation with different surfactant and sol-gel method. XRD patterns show that all the obtained samples are in cubic Gd2O3, and the results of FTIR and fluorescent spectra conformed that OP is a good surfactant for preparing the Gd2O3:Eu^3 phosphors. The SEM photographs show that the particles prepared by urea homogeneous precipitation method are all spherical and well-dispersed, and grain morphology can be controlled by different surfactant. XRD and SEM indicate that the particle sizes prepared by sol-gel method are in the range of 5-30 nm, and the grain sizes increase with increasing of heated temperatures. Luminescence spectra indicat that the main emission peaks of all samples are at 610 nm, the intensities are different from samples prepared with different surfactant and the luminescence intensities increase with increasing of annealed temperatures.     

Preparation and Luminescence of SrAi2O4:Eu2+, Dy3+ Nano-Particle

SrAl2O4: Eu2 , Dy3 nano-particle luminescence material was prepared by sol-gel method. Influences of synthesis conditions on the particle size and luminescence properties of SrAl2O4: Eu2 , Dy3 were studied. The synthesis process and the properties of the samples were analyzed by DTA, TGA, XRD, SEM. The result suggested that the formation of SrAl2O4: Eu2 , Dy3 sol is a slow heat release process beginning at 500 ℃ and peaking at 759 ℃.SrAl2O4: Eu2 ,Dy3 crystalline was formed at 1100 ℃. The luminescence properties of the SrAl2O4: Eu2 , Dy3 nanoparticle were compared with the conventional SrAl2O4: Eu2 , Dy3 particles. The average particle size of the product is about 30 nm. The excitation spectrum of the sample shows a broad band with peaks at 240, 330, 378 and 425 nm. The emission spectrum is a broadband spectrum with a peak at 523 nm.     

SrAl2O4:Eu, Dy Nanometer Phosphors Synthesized by Combustion Method

SrAl2 O4: Eu, Dy nanometer phosphors were synthesized by combustion method at 500 ～ 900℃, followed by heating the combustion sample at 1150℃ at a weak reductive atmosphere and nanometer phosphor with much better luminescent properties was obtained. The influences of the initiating combustion temperature, H3BO3 quantity, the mass ratio of urea and nitrate on the luminescent intensity of nanometer phosphors were studied. The optimum synthetic conditions were determined. The analysis results by transmission electron microscopy (TEM) indicate that the particle size of the synthetic product is less than 75 nm. The luminescent materials do not need to be ground. Their coating can be refined. It supplies a new approach to the rapid preparation of the luminescent materials at low temperature. The excitation and emission spectra indicate that the main peaks in the excitation and emission spectrum of nanometer phosphor synthesized by combustion method shifted to the short wavelength compared with the phosphor obtained by the solidstate reaction synthesis method. The reason of blue shift was explained. The afterglow decay results indicate that the decay speed of the afterglow for nanometer phosphor is faster than that obtained by the solid-state reaction method.     

SrAl_2O_4:Eu~(2+),Dy~(3+)的发光性质及机理

研究了Eu2＋、Dy3＋共激活的SrAl2O4体系的发光性能和能量传输。结果表明，Dy3＋、Eu2＋共存时，Eu2＋的发光强度远远大于无Dy3＋时的发光强度，证明Dy3＋对Eu2＋的发光有敏化作用。Dy→Eu2＋能量传输的方式为籍助于载流子的能量输运。     

Effect of mixing process on the luminescent properties of SrAl_2O_4:Eu~(2+),Dy~(3+) long afterglow phosphors

A new mixing method was developed for solid-state reaction synthesis of SrAl2O4:Eu2+,Dy3+ long afterglow phosphors.The morphology and crystal structure of the phosphors were analyzed with scanning electron microscope(SEM) and X-ray diffractometer(XRD).The excitation and emission spectra of the long afterglow phosphors were measured,and the main emission band was around 514 nm.The decay time of the product was measured and compared with the phosphors prepared using dry-mixing method and wet-mixing method.It ...     

Effect of Organic Solvent and Resin on Luminescent Capability of SrAl2O4:Eu2+, Dy3+ Phosphor

Organic substance such as solvent and resin's effect on luminescent capability of SrAl2O4:Eu2 , Dy3 phosphor was studied. Some organic solvents and resins were selected for experimentation. The results indicate that those organic solvents will not have negative effect on the applied capability of SrAl2O4:Eu2 , Dy3 phosphor. Adopting the organic resins and covering method, the afterglow luminance of SrAl2O4:Eu2 , Dy3 phosphor was increased by 85.01% and 82.51%.     

Synthesis of Long Afterglow Phosphors MAl2O4:Eu2+, Dy3+(M=Ca, Sr, Ba) by Microemulsion Method and Their Luminescent Properties

Long afterglow phosphors MAl2O4:Eu2 , Dy3 (M=Ca, Sr, Ba) were synthesized by microemulsion method, and their crystal structure and luminescent properties were compared and investigated. XRD patterns of samples indicate that phosphors CaAl2O4:Eu2 , Dy3 and SrAl2O4:Eu2 , Dy3 are with monoclinic crystal structure and phosphor BaAl2O4:Eu2 , Dy3 is with hexagonal crystal structure. The wide range of excitation spectrum of phosphors MAl2O4:Eu2 , Dy3 (M=Ca,Sr,Ba) indicates that the luminescent materials can be excited by light from ultraviolet ray to visible light and the maximum emission wavelength of phosphors MAl2O4:Eu2 , Dy3 (M=Ca, Sr, Ba) is found mainly at λem of 440 nm (M=Ca), 520 nm (M=Sr) and 496 nm (M=Ba) respectively, the corresponding colors of emission light are blue, green and cyna-green respectively. The afterglow decay tendency of phosphors can be summarized as three processes: initial rapid decay, intermediate transitional decay and very long slow decay. Afterglow decay curves coincide with formula I=At-n, and the sequence of afterglow intensity and time is Sr＞Ca＞Ba.     

SrAl2O4 :Eu2+, Dy3+ Long Afterglow Phosphors Prepared by Chemical Coprecipitation Method

SrAl2 O4: Eu2 , Dy3 long afterglow phosphors were prepared by chemical coprecipitation method. Ammonium carbonate and ammonium hydrogen carbonate were used as the precipitants. The preparation of the SrAl2 O4: Eu2 ,Dy3 precursor was completed at room temperature by controlling the concentration of the metal-salt solution, pH value of the system, etc. The phosphors were prepared by sintering the precursor at 1000 ～ 1200 ℃ in a weak reducing atmosphere for 2 h. The XRD, SEM, excitation spectra, emission spectra and afterglow decay of the samples were tested and the optimal synthesis conditions of the SrAl2O4: Eu2 , Dy3 long afterglow phosphors prepared by precipitation method were determined. The phosphor which had good luminescent properties is prepared and its persistent time can reach more than 1600 min. In the coprecipitation process, a small amount of glucose operates to refe the luminescent powders. The particle size of the phosphor can be less than 1 μm. The sintering temperature of the sample prepared by the coprecipitation method is much lower than that of the one prepared by the high temperature solid state method.Compared with the high temperature solid state method, a clear blue shift occurs in the excitation and emission spectra of the samples.     

Investigations into thermoluminescence and afterglow characterization of strontium aluminates with boron-modification and reductions via sol-gel route

The effects of strontium aluminates of SrAl2O4:Eu2+,Dy3+(SAED) and boron-modified SAED (BSAED) phases synthesized from a sol-gel process on thermoluminescence (TL) along with their afterglow properties were systematically investigated with thermal activation in the different atmospheres. The result showed that the addition of boron and the reduction routes of Eu3+to Eu2+ in SrAl2O4:Dy3+were related to phosphorescent decay properties. The aid of Dy3+to induce the hole-trapping effect required both SAED and BSAED to be heated at 1300°C under the H2/N2(5%:95%) atmosphere. However, the trapping behavior of the reductions of SAED in nitrogen was similar to the compound without Dy3+co-doping SrAl2O4:Eu2+ (SAE) in H2/N2(5%:95%). BSAED showed deeper traps in situ compared to SAED which contained no boron, and this led to the better afterglow properties of BSAED than those of SAED. The afterglow spectrum of BSAED showed two peaks at 400±1 nm and 485±1 nm, which were two individuals composed and contributed from different depths of traps at 0.57 and 0.76eV, accordingly. The depth of the traps was calculated from the Hoogenstraaten’s plot of glow curves. The calculations for SAED and SAE were at around 0.43 and 0.18eV, respectively.